1. Field of the Invention
The present invention relates to a magnetic head device, a magnetic recording/reproducing apparatus, and a tape drive system using the magnetic head device. More particularly, the present invention relates to a technology which makes it possible to increase recording density as a result of making it easy to dispose a plurality of magnetic heads (here and hereunder refers to magnetic recording heads and magnetic reproducing heads).
2. Description of the Related Art
In recent years, to realize a higher capacity magnetic recording medium, higher density recording is demanded of magnetic heads. Accordingly, magnetic heads that are suitable for reducing the widths of recording tracks are used.
When high-density recording is performed, a more precise track servo operation is performed. In general, a plastic material is used for a substrate of a magnetic tape itself. Therefore, taking into account deformation resulting from long-time storage, in an AIT-3 format, which is currently in practical use, it is assumed that tape bending is at least 15 μm compared to a track width of 5.5 μm. The AIT-3 format is discussed in, for example, non-patent document 2: “Standard ECMA-329, 8-mm Wide Magnetic Tape Cartridges for Information Interchange-Helical Scan Recording-AIT-3 Format (December, 2001), http://www.ecma-international.org/publications/standards/Ecma-329.htm”
Accordingly, a powerful track servo operation is performed. In general, a system that uses what is called a “double azimuth method” for allowing slight servo displacements and that does not allow a signal to be reproduced even if the servo operation is performed on an adjacent track is put into practical use.
In a linear tape system, in an Ultrium-1 format (that is discussed in, for example, non-patent document 1: “Standard ECMA-319, 12.7-mm-384-Track Magnetic Tape Cartridges-Ultrium-1 Format (June, 2001), http://www.ecma-international.org/publications/standards/Ecma-319.htm”), a track pitch is set at 27.5 μm as a result of previously recording a servo signal. However, in a format which is a continuation of the Ultrium-1 format, the setting of the track pitch is limited to approximately 15 μm.
Accordingly, when a linear serpentine method is performed, an on-track reproducing system is not established unless mechanical precision is increased and a powerful servo operation is performed. Therefore, it is becoming difficult to increase recording density at a lower cost by providing a technology that is merely a continuation of the related art.
Accordingly, for a helical scanning system in which a track pitch has been reduced earlier, to overcome the problem of the difficulty of performing a reproduction servo operation due to the reduction of a track width, what is called a “non-tracking system” is proposed and is put into practical use.
Technologies that are discussed in U.S. Pat. Nos. 1,842,057, 1,842,058, and 1,842,059 are patented technologies that serve as the fundamentals of a non-tracking method. According to the technologies, since an identification operation is performed on the basis of divided blocks with respect to tracks subjected to double azimuth recording by helical scanning, when data is recorded, the data can be reconstructed even if data of a target track is not reproduced by one operation. Accordingly, these technologies allow a margin that is at least four times that of a track controlling operation performed within one track that is used in a related track servo operation.
Japanese Unexamined Patent Application Publication Nos. Hei 04-370580 and Hei 05-20788 propose a signal recording method that assumes a reproducing operation by the non-tracking method.
Studies are conducted to find out whether the non-tracking technology can also be used in linear recording in addition to in helical scanning. The use of the non-tracking technology in linear systems is beginning to be proposed as in, for example, Japanese Unexamined Patent Application Publication Nos. Hei 10-283620 and 2003-132504.
To achieve high-capacity and high-density magnetic recording, it is desirable to provide a plurality of channels. Accordingly, there is a demand for providing a plurality of magnetic heads.
For example, one type of magnetic head device having a plurality of magnetic heads is proposed. In this magnetic head device, a plurality of magnetic recording head elements or magnetic reproducing head elements are laminated on one head substrate through, for example, a magnetic shield layer and an insulating layer.
More specifically, a magnetic head device that is proposed in Japanese Unexamined Patent Application Publication No. 2002-216313 is a magnetic recording head device, and a magnetic head device that is proposed in Japanese Unexamined Patent Application Publication No. 2002-157710 is a magnetic reproducing head device.
In each of the magnetic head devices, a plurality of magnetic recording head layers or magnetic reproducing head layers, each having one magnetic head element, are placed upon a substrate formed of a non-magnetic material, and all of the magnetic head elements are formed so as to be shifted in a direction that is substantially perpendicular to a lamination direction (the shift direction will hereunder referred to as “head width direction”).
Accordingly, a plurality of magnetic heads can be disposed, and can be placed near each other or can overlap each other in the head width direction, so that it is possible to reduce the widths of recording tracks.
In related linear systems, from the viewpoint of transfer rate, the use of a plurality of tracks is being pursued. However, from restrictions of a magnetic recording medium that is used, recording is not performed on adjacent tracks at the same time. As discussed, for example, in “12.9 Location of datatrack” on page 58 of non-patent document 1, since eight heads are disposed so as to be separated by 12 tracks (333 μm), when performing recording on a tape, the recording is simultaneously performed on tracks that are separated by 12 tracks, but writing is not performed on adjacent tracks at the same time.
This means that writing of signals on adjacent tracks is performed as a result of mechanically shifting the writing positions. Therefore, although the writing operation is performed on eight tracks, it is substantially performed on tracks that are separated by 12 tracks, as a result of which the writing operation on the adjacent tracks is performed at a completely different timing. Consequently, the writing operation depends upon mechanical precision. This is a technical obstacle to increasing recording density by reducing track pitch.
FIG. 17 is a schematic view showing the relationship between the position of linear tape recording tracks and magnetic heads in a related art. Reference numerals 1 denote tracks that are formed parallel to tape transport directions on a magnetic tape 2.
Reference numeral 3 denotes a head block. Recording heads 4 and reproducing heads 5 are at a surface of the head block 3 that slides with respect to the magnetic tape 2, and oppose the tracks 1.
The recording heads 4 in a same layer are provided so as to be separated from each other by approximately 100 μm in a tape width direction. This is because, due to the amount of space occupied by lead wires and coils of the recording heads 4, the recording heads 4 in the same layer are to be separated by a predetermined interval (such as by 12 tracks).
In FIG. 17, for explanation purposes, the three tracks 1 that are used for one writing operation are only shown. However, actually, when writing operations are performed on the entire length of the tape while transporting the tape and a tape end is reached, the head block 3 moves either upward or downward to perform writing operations again, so that gaps are filled with tracks. (This method is called the “linear serpentine method.”)
Therefore, writing of adjacent tracks is performed at a different timing and depends upon mechanical precision. Consequently, recording density is not increased as a result of reducing track pitch.
In the related art, when performing high-density recording, as discussed in, for example, “13.1 Track Configuration” on page 62 and FIG. 40 of non-patent document 2, the following is possible. By setting two recording azimuth directions, in a reproducing operation, heads having the same azimuth angle are capable of reading data, but heads having a different azimuth angle are not capable of reading data.
Accordingly, for example, even if guard bands are not provided, misalignment with respect to a track during a reproducing operation occurs, and a mechanical error corresponding to substantially one track, occurring up to a time tracks of the same azimuth angle are scanned by a head, occurs, it is possible to prevent reading of a signal of a wrong track, so that a large mechanical precision margin is provided. Therefore, even if the track pitch is small at 5.5 μm in the format discussed in the non-patent document 2, the system is established.
However, when the track pitch is reduced to further increase recording density, and overwriting is performed with an azimuth head, leakage magnetic flux that is generated perpendicularly to the head transport directions from a head gap when performing a recording operation with a head having a particular azimuth angle causes previously recorded data to be erased. This is an obstacle to achieving high-density recording as a result of reducing track pitch of a magnetic tape.
Many proposals for achieving more efficient recording operations as a result of providing a plurality of recording heads with respect to one unit have been provided in the past as in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-132504, 2005-11456, 2004-246949, 2003-338012, 2003-123214, 2002-216313, 2001-229516, Hei 2-42612, Sho 58-220218, Sho 63-106909, and Sho 52-128114, and Japanese Patent No. 3375339. However, in the documents other than Japanese Unexamined Patent Application Publication Nos. 2005-11456, 2004-246949, 2003-338012, 2003-123214, 2002-216313, and 2001-229516, recording density is not considered in view of the present situation, that is, structures in which data recording/reproducing speed is given priority over high-density recording are provided. Therefore, these structures may be substantially difficult to use in an area in which track width is equal to or less than 10 μm.
Japanese Unexamined Patent Application Publication Nos. 2005-11456, 2004-246949, 2003-338012, 2003-123214, 2002-216313, and 2001-229516 primarily propose multi-head systems where the use of helical scanning systems is assumed. Japanese Unexamined Patent Application Publication No. 2003-132504 considers systems that are characteristic of those using the linear method, but primarily relates to reproducing operations.